Catalytic dehydration and dehydrogenation process



Patented Jan. 31, 1933 amen snow 2'.

F WIPLMINGaH This invention relates to catalytic processes of dehydrogenation and dehydration of organic compounds wherein an oxide catalyst is used together with a substance that has the efiect of repressing either the dehydrogenation or dehydration.

in the field of organic chemistry, the production of numerous important compounds depends on the ease and completeness with which a molecule of hydrogen or one of water may be detached from a single molecule or from two difierent molecules of more available or less costly compounds. Such reactions are conveniently termed dehydrogenations or dehydrations, depending on the minor products of reaction and together constitute two of the most important classes of organic reactions.

Dehydrations are necessarily restricted to any ear-containing compounds, the prepan of others or oletins from alcohols being familiar examples. In general, condensations which take place with the elimination of water may be considered dehydrations. As examples of such condensations by dehydration, the formation of mesityl oxide and phorone from acetone and the preparation of ethers from alcohols may be cited. Dehydrogenations are broader in their apnlieation because hydrocarbons and'other non-oXygen-containing organic compounds may be dehydrogenated as Well as com-- pounds containing the hydroxyl group. The

terms dehydrogenation and dehydrogenation reaction as used throughout the specification and claims are intended to exclude oxidation reactions in which oxygen or its equivalent is caused to react with hydrogen containing compounds to form reaction products containing a less amount or" hydrogen. The mechanism of oxidation reactions of this type is entirely different from that involved in reaction wherein hydrogen atoms are split off from hydrogemcontaining compounds to produce molecular hydrogen. The removal of hydrogen from cyclohexanol to form phenol is a familiar example of the detachment of hydrogen directly linked to carbon, While the preparation of acetaldehyde from ctha- QAEEN'IT OFFICE RSI-BY, AND WILBUR A. LAZIEB, 42:5 DU PONT DE NEMOURS & COMPANY, d? 05 DELAWARE CATALYTIC DEHYDROGENATION PROCESS 1926. Serial No. 118,358.

nol, or acetone from isopropanol illustrates dehydrogenation of the hydroxl group.

It is Well known that in order to bring about a practical speed of dehydrogenation or dehydration, the process must be conducted at elevated temperatures so the reactions are usually carried out in the vapor phase. The use of certain catalysts or porous inorganic solids possessing extensive surfaces also greatly facilitates the reactions. As most catalytic masses are not strictly specific in their action, the conditions necessary for operation tend to aggravate the undesired side reactions. it is particularly diliicult to select contact materials which Will cause only dehydrogenation or dehydration of alcohols, the greater number being more or less mixed in their behavior. In certain cases it has been found that the more active catalysts are often mixed catalysts while the pure catalysts possess very inferior activity.

s has been mentioned, one of the most important and familiar uses of dehydrogenation and dehydration reactions is in treating alcohols to obtain ethers, a1dehydes,'ketones or olefins. When subjected to dehydrogenating influences, primary alcohols yield aldehydes and secondary alcohols yield. ketones, the other product, of course, being hydrogen. Tertiary alcohols are not capable of dehydrd genation and undergo only dehydration.v Methanol is dehydrated to dimethyl ether, While all other alcohols readily yield unsaturated hydrocarbons under the influence of dehydrating catalysts.

It is known that reduced metals such as copper, iron, or nickel are especially eliicacious for the strict dehydrogenation of alcohols, so vigorous in their action that but often are the aldehydos or ketones formed are split up with the formation of carbon monoxide and saturated hydrocarbons. Other disadvantages of these metallic catalysts are their lysts for the dehydrogenation or dehydra- 10G tion of alcohols. For example, the oxides of aluminum and thorium have marked dehydrating properties. Others such as magnesia are predonnnatingly dehydrogenating, while still others such as chromium oxide giving mixed reactions are scattered between these. Sabatier (Catalysis in Organic Chemistry) has arranged the non-reducible oxides in order of their tendencies to dehydrate or dehydrogenate alcohols, but recent investigators have shown that such a rigid classification is not valid, as the behavior of the catalytic oxide is dependent in part on its method of reparation.

ccording to the present invention, the dehydrogenating or dehydrating character of oxide catalysts may be profoundly altered by the addition of small amounts of substances which of themselves may have little or no efiect on the reaction. l ve have found in particular that the alkali and alkali earth metals in the form of their oxides, carbonates, hydroxides, or salts with feeble acids such as organic acids, exercise a marked repressing effect on the dehydration reactions while strongly acidic oxides in the form of acids, ammonium salts or anhydrides have a similar efiect in repressin dehydrogenation. Zinc oxide which norma ly gives about 5% of dehydration and dehydrogenation, hecomes a dehydration catalyst by the addition of 10% of zinc sulfate. In a similar mannor, the 5% of dehydration normally present entirely disappears after the addition of a few percent of sodium carbonate to t. e catalyst. This invention now makes it possible to select a suitahle'catalyst from the standpoint of durability, activity, and insensitivity to poisons, and then so to alter the qualitative performance of the mass as to suit the needs of the process in question. Tie have found that the effect of carbonates, oxides, or hydroxides of alkali or alkali earth metals, or of acid oxides in general in its application and that the qualitative behavior of any oxide catalyst is altered by the addition of any base, or of any oxide markedly more acidic than the oxide treated.

Most oxide catalysts that can be used for the dehydrogenation or dehydration respectively of organic compounds, do not have a single efiect, that is, they do not cause the re action to proceed entirely in the desired direction but give rise to a mixed dehydrogenation and dehydration. Among such oxide catalysts may be named. the following: the oxides of berryllium, magnesium, zinc, aluminum, silicon, titanium, germanium, zirconium, tin, cerium, thorium, vanadium, blSIllllL-ll, chromium, molybdenum, tungsten, uranium, man-- ganese, iron, or any of the rare earths, etc. Each oxide has its own peculiar normal effect in the reaction as regards the relati e proportions or moles of dehydrogenated and dehydrated product produced. This eilect can be changed and controlled by the addition to the oxide catalyst of another substance may itself have no effect on the reaction which, nevertheless, will exert a very found eil'eet on the catalyst, ausing it t selectively so as to repress or suppress one the dehydrogenating or dehydra' tions taking place. This repression o the dehydrogenation ,or dehydration, as

the art so that there not only was no possible control of such reactions in the desired direction, but there was also no practical means utilizing any desired oxide catalysts in" particular reaction. We accordingly des nate these substances having such repress? or suppressive eilects by the general term repressers or repressives, indicating thei that the action may be either p.- 1 i I plcte in eliminating one of the (to ing or dehydrating effects, While w by the term suppressor or suppres c substantially total repressive effect. repressers are neither to considered ponents or constituents of mixed nor are they to he considered pronn putes may, in special cases, also be 'nresen.- incidentally. A Such oxide catalysts as enumerated may he "treated with a compound of one of the alkali or alkali earth metals of groups it the Periodic Table, either infthe oxides, carbonates, hydroxides,

entireiv 'tlClllZll ca tirelv, i

trate the idea it fofliii When the vapor I 'z over catalyst heated of zinc oxide prepared liy of zinc oxalate, tor every reacting there are produce: of propylene and shou W But if the zinc oxide is triturated with a solution of sodium carbonate and dried in such a manner that the product contains 4.5% of sodium carbonate, the olefin obtained per mole of alcohol reacting is less than .01 molessand the acetone produced more than .99 moles. If, instead of sodium carbonate, about 7% of zinc sulfate is added to the zinc oxide, there are produced about 60 moles of propylene to every 40 moles of acetone. 1

Example 2 A uranium oxide catalyst prepared by the reduction of UO with alcohol produces from ethanol at 400 C. about .25 moles of acetaldehyde for every mole of ethylene formed. After mixing the uranium oxide with 10% of its weight of potassium carbonate, there are produced with every mole of ethylene, 10 moles of acetaldehyde.v On the other hand, 15% of boricacidad'ded to the catalyst reduces the proportion of acetaldehyde formed to .09 moles per mole of ethylene. A

By the use of the terms repressive agents and suppressive agents we refer to the ultimate or final effects of these added substances and not to any theory or mechanism of operation, or to any explanation of the ionic, molecular, or atomic relationships or groupings on the surfaces of the catalyst, which may or may not favor preferential, selective, or other action whose ultimate effect is the repression referred to above.

We claim:

1. The process of dehydrogenating an oxygen containingorganic compound capable of dehydrogenation which comprises passing said compound, in the absence of any compound which will react therewith, in contact with an oxide catalyst having both a dehydroenating and a dehydrating efiect, said catalyst having admixed therewith an alkaline compound of an alkali metal which represses the dehydrating effect of said oxide catalyst. 2. The invention described in claim 1 in which the alkaline compound exerts a total repressive efiect.

3. The invention described in claim 1 in which the repressive agent is an alkaline oxide under the conditions of operation.

4. The invention described in claim 1 in which the catalyst contains a diflicultly reducible oxide.

5. In a catalytic process of dehydrogenating an organic compound in the absence of other substances which will react therewith wherein an oxide catalystis employed that has both a dehydrogenating and a dehydrating effect, the step of repressing the dehydrating effect by adding to said catalyst a basic compound of a metal of the group consisting of the alkali and alkaline earth metals.

6.'In a catalytic process of dehydrogenating an alcohol in the absence of other substances which will react therewith wherein an oxide catalyst is ample ed that has both a dehydrogenating and a ehydrating effect, the ste of repressing the dehydrating effect by ad ing to said catalyst a basic compound of a metal of the group consisting of the alkali and alkaline earth metals.

7 In a catalytic process of dehydrogenating'a secondary alcohol in the absence of other substances which will react therewith wherein an oxide catalyst is employed that has both a dehydro enating and a dehydrating eifect, the step 0 repressing the dehydrating effect by adding to said catalyst a compound of a metal of the group consisting of the alkali and alkaline earth metals.

8. In the catalytic process of dehydro genating isopropyl alcohol to form acetone wherein an oxide catalyst is employed that has both a dehydrogenating and a dehydrating effect, the step of repressing the dehydrating effect by adding to said catalyst a compound of an alkali metal.

9. In the process of dehydrogenating isopropyl alcohol to form acetone wherein a zinc oxide catalyst is employed which has both a dehydrogenating and a dehydrating eifect and wherein propylene is normally formed due to the dehydrating effect of said catalyst, the step of repressing the formation of saidpropylene by adding an alkali metal compound to said catalyst.

10. The process of claim 9 in which the alkali metal compound is sodium carbonate.

In testimony whereof we afiix our signatures.

HUGH STOTT TAYLOR. WILBUR A. LAZIER. 

